Additional research looking at right hemisphere lesions has demonstrated that the right hemisphere is responsible for some linguistical functions: finding that patients with such lesions may be ‘impaired relative to normal controls on certain tests of language’ (Corballis, C. M. 1983, p. 33). One study by Lesser (1974) reported such an impairment ‘on a semantic test involving comprehension of spoken words but not on a phonological or syntactic test’ (Corballis, C.M. 1983, p.33), suggesting a small role for the right hemisphere in language processing.
Kinsbourne and McMurray carried out valuable research using healthy participants, using a procedure similar to the current study (cited in Kalat, 2004, pg. 427). They asked participants to tap with a pencil on a piece of paper as many times as they could in one minute, first with their right hand then with their left, then asked them to do the same again whilst talking, they found that ‘for most right-handers, talking decreases the tapping rate with the right hand more than with the left hand’. This further supports left hemispheric dominance for language, as well as supporting the current study’s methodology and informing its hypothesis.
As has been demonstrated most research supports left hemispheric dominance of language functions, but also links hemispheric specialisation with other factors and accepts that the right hemisphere holds some language comprehension control.
This experiment looks for further supportive evidence and also briefly looks at handedness as a possible affecting factor.
The study uses a finger tapping and language processing task, with the notion that the speed at which keys are pressed will be relatively similar with both hands. If however, if it is the case that language is more associated with the left hemisphere, then on average when processing language, the speed of the right hand will be slower than the left hand, presumably because the left hemisphere then has to do two tasks at once (right hand finger tapping and language processing). This is only the case however if all participants in the experiment have left hemisphere dominance for language, and is thus the reason we have recorded the handedness of our participants.
As a result of previous studies and research the hypothesis for this experiment is: there will be differences in the number of taps made from each of the two hands when language is or isn’t being processed.
Method
Design
The experiment used a fully repeated measures within-subjects design: all participants took part in all conditions. There was one independent variable, consisting of four different levels: left hand, talking, no talking and right hand talking, no talking. The dependent variable was the number of key presses made within the time limit of 30 seconds per trial.
Participants
All participants were undergraduate psychology students from the University of Portsmouth who collected their own time data from the four trials. Tapping scores from 20 students (including the experimenter’s own) were then collected using an opportunity sample and collated. Participants had a mean age of 30.9 years, a range of 28 years, and a standard deviation of 10.5 years .All were female, two of which were left handed (For raw data see Appendix 1).
Materials
The experiment used an interactive CD-ROM that had the task used already programmed onto it (Kalat, Exploring Biological Psychology, Thomson and Wadsworth, 2004). The CD was provided with the course textbook (Kalat Biological Psychology 8th edition, Thomson and Wadsworth, 2004). A computer keyboard was used as a response device.
Procedure
Participants were seated in front of a computer screen, asked to fill in an informed consent form and provided with standardised instructions as to how to carry out the task (See Appendix 5).
Each participant was instructed to make as many key presses on the keyboard as they could within 30 seconds. First participants were given two practice trials, and then four experimental trials. In the experimental trials they were required to tap with a finger from their right hand and then with a finger from their left hand. In the two other trials they were required to tap with their right hand and then their left hand at the same time as answering some simple questions.
The number of key presses made during each of the trials was recorded by the computer program.
The experiment took no longer than five minutes, and following the experiment participants were provided with a debriefing form (see Appendix 4) telling them of the main objectives of the study.
Results
Descriptive Statistics
Figure 1 below shows that the mean numbers of key presses differ for each hand when language is or isn’t being processed: thus supporting our hypothesis. The mean number of taps recorded decreased for both hands when talking during the task.
However, it can also be seen that the mean number of key presses recorded with the left hand when talking (165) are less than those recorded with the right hand when talking (179.6), this does not support the hypothesis of left hemisphere language dominance.
Mean Number of Key Presses per Condition
Figure 1.
Inferential Statistics
In order to test the significance of the results, a repeated measures within-subjects ANOVA was carried out. This was used because we wanted to test for a significant difference between all four levels of the independent variable where the same participants were used for all the conditions, an ANOVA allows for this comparison.
Figure 3. ANOVA Summary Table:
*p<. 05
The ANOVA produced the following result:
(F 3, 57 (α = 5%) = 3.74, p<.05) therefore reject Ho
A significant difference was found between the four conditions. This supports the hypothesis: the number of taps made from each of the two hands differed significantly across the conditions when language was or wasn’t processed (language task was present or absent).
While the repeated measures ANOVA shows us that there are differences among the conditions that cannot be attributed to error, it does not tell us whether these differences are practically important. Eta squared is the method used to examine the experimental effect, and is calculated as the ratio between the effect of the independent variables and the total variance. The Eta squared test showed a 2.8% importance, demonstrating that very little of the variation in the number of key presses recorded can be attributed to differences in the independent variable, thus the results were not important in a practical setting.
Discussion
The main findings from the study support the hypothesis: significant differences were found across the four levels of the independent variable. The number of key presses made differed significantly from each of the two hands across the four trials, i.e. there was a significant effect of hemisphere and task present/task absent.
However, through looking at and comparing the means we can see that this significance is unlikely to lie between the conditions that our left hemisphere language dominance theory would have predicted. This is not in agreement with previous research mentioned in the introduction.
The mean number of key presses for the right hand with talking was greater than the mean for left hand with talking. This is not what we would have expected if the left hemisphere was having to be responsible for the processing of two tasks (controlling the taps of the right hand and language), and thus does not support left hemispheric specialisation for language. However, we have not tested the significance of this difference, so therefore this result may have occurred by chance and is thus not an accurate predictor of hemispheric specialisation.
The results did however support the idea that our hemispheres find doing two tasks simultaneously harder than when carrying out one task at a time – the means for both hands decreased when talking was added as an extra task alongside key pressing.
A possible reason for our mean results not supporting our predictions can be explained by handedness. The means of left and right hand without talking differ greatly for the participants - most of whom are right-handed. Thus perhaps handedness is affecting the number of key presses made. It is possible that our belief that the number of taps made by each hand would be similar without talking is incorrect; this could be explained by the amount of everyday usage/practice the participants’ dominant hand gets. I am a left hander and find it much easier to do certain things quicker or more accurately with my left hand than I do my right; perhaps this factor or something similar is affecting the results of this experiment. In order to further investigate and support this theory we would have to test for a significant difference between these means using a post hoc comparison such as an LSD or Tukey HSD test.
Additionally perhaps the left handers in the experiment were right hemisphere dominant for language, or a mixture of left and right: as stated by Basso & Rusconi, 1998, cited in Kalat, 2004, p. 430 ‘left-handers are more variable – most left-handers have left-hemisphere dominance for speech, just like right handers, but some have right hemisphere dominance or a mixture of left and right’, the left handed participants may have thus found tapping whilst answering the questions easier when using their right hand. However, it seems unlikely to be an affecting factor as only 2 out of the 20 participants were left handed, although it may explain why the observed effects were not very big.
We can also look to research into the right hemispheres involvement in language when explaining our results, perhaps for some people, or perhaps even in general, the right hemisphere is more involved than previously thought, this would explain our conflicting means and should be investigated further.
Even though our results do not support left hemispheric language dominance, we should not suddenly decide that it should be rejected; much research is supportive and a repetition of this study may be also.
We must also consider methodological issues when discussing the results.
Firstly, subject selection: was having all female, undergraduate psychology students as participants a representation of the wider population? I think not, however this is also not necessarily important, as research has found no real evidence for sex being a contributing factor: ‘there is little evidence to support the view that hemispheric specialisation is different in males and females’ (Butler, 1997, p.187). Additionally it is unlikely that knowledge of psychology affected such a mechanical task as that which was used.
Another possible issue is the design, using the same participants across the conditions did control for the effects of individual differences but not practice effects and order effects which may have played a role. The final two trials were the most important ones in the task and it is possible that by this time participants had become bored or tired. To avoid these problems in any future study, trials could be shorter or have longer breaks and the order of conditions counterbalanced across the participants.
Another question involving the procedure is whether key presses and simple questions are an accurate measurement of such a complex thing as hemispheric specialisation?
As the Eta Squared test shows, the results cannot be deemed important in a practical setting and thus provide no real implications for the real world. To improve this future research could repeat the study using a more representative population and possibly remove the variable of handedness i.e. have equal amounts of left and right handers, or find a way of measuring its affect.
In conclusion this study showed that participants made significantly different numbers of key presses across the four levels of the independent variable, supporting the experimental hypothesis. However, the means do not support the more specific idea of left hemisphere dominance for language (more key presses were recorded for the right hand with talking than the left). This does not mean that all theories should be overturned as much research does support this theory; moreover it suggests that further research needs to be carried out, particularly with ‘normal’ participants, in order for us to understand how general hemispheric specialisation patterns concerning language are.
References
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Butler, S.R. (1997). Hemispheric specialisation and neuronal plasticity [electronic version] Developmental Brain Dysfunction, 10: 187-202.
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Corballis, C. M. (1983). Human Laterality. London: Academic Press.
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Kalat, J. W. (2004). Biological psychology (8th edition). Canada: Thomson and Wadsworth.
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Springer, S.P., Deutsch, G. (1998). Left brain, right brain: Perspectives from Cognitive Neuroscience (5th ed). New York: W.H. Freeman and Company.
APPENDIX
Appendix Index
1: Raw data sheet
2: Calculations
3: Standardised Instructions
4: Informed consent form
5: Debriefing form
Appendix One
Raw Data
Appendix Two
Statistical Calculations
Simple repeated measures ANOVA
Raw Data Summary Values Table
SS Total: Sum of Squares
∑χ2 - = 2876234 -
= 2876234 – 2581211.25
= 295022.75
SSBS
= + ….. - 2581211.25 = + …… = 2824587.5 – 2581211.25
= 243376.25
SSWS
SS Total – SSBS
= 295022.75 – 243376.25
= 51646.5
SSBT
= +
= 646201.25 + 544500 + 753884.45 + 645123.2 – 2581211.25
= 2589708.9 – 2581211.25
= 8497.65
SSResidual
SSWS - SSBT
= 51646.5 – 8497.65
= 43148.85
Degrees of Freedom
df Total = N -1 = 79
df BS = p-1 = 19
df WS = N-p = 60
df BT = k-1 = 3
df Residual = (P-1) (k-1) = 57
Mean Squares
MsBs = SSBS/dfBS
= 243376.25/19
= 12809.27632
MsWs = SSWS/dfWS
= 51646.5/60
= 860.775
MsBT = SSBT/dfBT
= 8497.65/3
= 2832.55
MS Residual = SSRes/dfRea
= 43148.55/57
= 756.9921053
F Value = F = MsBT/MS Residual
= 2832.55/756.9921053
= 3.741848799 = 3.74
Eta Squared calculations
N2 = SS effect/SS total
= 8497.65/295022.75
=0.028
= 2.8%
Appendix Three
Standardised Instructions: (As appeared on CD program –Kalat, 2004)
The following exercise should demonstrate some differences between your two hemispheres. In each of the 6 trials that follow, once you hear a tone, tape any key on your keyboard as quickly as you can until you hear the tone again. For each trial you will be instructed which hand to use. The first two trials are practice. For each of the other trials you will tap for 30 seconds. In half of these trials you will also be asked some questions. Answer those questions out loud as quickly as you can whilst continuing to tap.
